As the deadline for the UNAIDS 90–90–90 target approaches, huge challenges in HIV
diagnosis, access to treatment and follow up have become evident. This initiative
aims to have 90% of people living with HIV diagnosed, 90% of diagnosed people receiving
antiretroviral therapy (ART) and 90% of people receiving ART under viral suppression
by 2020 (http://www.unaids.org/sites/default/files/media_asset/90-90-90_en_0.pdf,
n.d.). In this regard, huge improvements have been made on ART programmes around the
world, especially in resource-limited settings. Nevertheless, identifying new and
undiagnosed HIV infections is an important issue in large areas of the world where
stigmatization and ignorance towards HIV infection and its transmission routes still
prevail. This is the case of most Latin American countries, which generally present
concentrated epidemics with a wide variety of epidemiological scenarios, most of which
are characterized by late presentation of individuals living with HIV to clinical
care (Crabtree-Ramirez et al., 2011). In Mexico, a middle-income country with a strong
ART programme, it is estimated that more than half of HIV-infected individuals are
unaware of their serologic status (http://www.censida.salud.gob.mx/descargas/2009/VIHSIDAenMexico2009.pdf,
n.d.). Cases like this render ART programmes alone unable to control the epidemics
and constitute a major challenge for the ambitious 90–90–90 target to become a reality.
Knowledge on HIV transmission dynamics is needed in order to focus and strengthen
prevention and early detection programmes, urgently needed in Latin America. In recent
years, HIV phylogenetic and phylogeographic analyses have been ever more recognized
as a fundamental tool for studying HIV transmission dynamics, which can result in
the generation of public health policies improving HIV prevention programmes (Grabowski
& Redd, Mar 2014). Phylogenetic and clustering analyses can provide useful information
on clinical and demographic factors shaping HIV transmission in specific geographic
areas, and when geographic data is available, can identify the specific location and
spread of HIV transmission hotspots. Large multinational efforts such as PANGEA-HIV
(Pillay et al., Mar 2015) have been created to use viral sequence data to assess transmission
of HIV in the context of generalized epidemics. Moreover, recent studies have demonstrated
the possibility of identifying HIV transmission hotspots in near real time by the
secondary phylogenetic analysis of HIV sequences obtained for routine drug resistance
testing in concentrated epidemics with a high sampling density (Poon et al., 2015).
In this issue of E-Biomedicine, Mehta et al. (Mehta et al., 2015) present a phylogeographic
study to assess the characteristics of HIV transmission in the Tijuana–San Diego crossing
of the Mexico–U.S. border region. This work is a good example of how phylogenetic
and phylogeographic analyses on already existing HIV sequence data can provide useful
information on HIV transmission dynamics in an especially complex HIV transmission
hotspot. The Tijuana–San Diego border is probably the busiest land border crossing
in the world, characterized by a large transnational commercial sex network, a large
population of people who inject drugs (PWID), and a large population of men who have
sex with men (MSM) (Strathdee et al., 2012). The prostitution district in Tijuana
is frequented by thousands of U.S. and foreign tourists each year and this region
geographically overlaps with a neighbourhood known for its high density of PWID. Risk
behaviour for HIV acquisition is high in the border region and is strongly associated
with economic disparities, with a high frequency of male clients negotiating condom-less
sex with female sex workers (FSW), who accept higher rates for unprotected sex out
of economic necessity and are also often PWID (Strathdee et al., 2012, Martinez-Donate
et al., 2015, Robertson et al., 2014). In their study, Mehta et al. describe the epidemics
in Tijuana and San Diego as highly separated, the last one dominated by MSM clusters.
Nevertheless, the authors identified bidirectional mixed international clusters including
FSW, PWID and MSM, describing this border region as a “melting pot” of risk groups.
International clusters had higher proportion of females, heterosexuals and PWID, highlighting
the importance of commercial sex in HIV transmission across the border and pointing
areas of opportunity for prevention interventions. Moreover, albeit with considerable
overlap in both directions, a shift in viral migration from Tijuana to San Diego was
observed comparing 2014 to the 1990s, when the opposite was true. It is important
to mention that even with a relatively low sampling density, clusters providing useful
epidemiological information were found yielding useful conclusions to inform public
health policies. Also, the lack of male individuals in clusters including FSW is also
informative as it underscores the need to focus detection efforts in their customers
and partners.
Following WHO recommendations to implement HIV drug resistance (DR) surveillance in
the region, many Latin American countries are making efforts to implement HIVDR surveys
nationally, with the support of WHO-accredited national and regional laboratories.
Thus, even with an important limitation in sequencing capacity, generation of HIV
sequence data linked to basic socio-demo-geographic data is expected to grow significantly
in the next few years. These data could also be used in phylogenetic and transmission
network analysis to inform HIV transmission dynamics in the region, always with a
cautious interpretation due to sampling limitations. Eventually, these data could
improve targeting of prevention and early detection efforts to place this region of
the world closer to the 90–90–90 target in 2020.
Disclosure
The authors declare no conflicts of interest.